Lighting a model with LEDs using a USB power connection

[Rumblestripe]

I'm looking at building the Bandai Millenium Falcon in the near future and I have an idea for lighting the model.

USB computer connections (also used for charging phones and tablets) deliver 5.0V and 1.0A (or 2.0-2.4A on "quickchargers"). You get four connections +5V, ground and two data. My idea would be to wire the lighting to a micro USB socket (they're tiny, the size you will find on most mobile phones - except Apple) and that would enable me to power the model either by plugging into a mains charger, a computer or a smaller battery pack with three AAA or AA cells. By using the two "data" connections as switchable power feeds I could have three independently operable lighting circuits. I'm thinking cockpit, engines and interior/loading bay. It also means that I have no permanent cable running from the model or need to create a battery compartment.

Has anyone done this or something similar? What resistors will I need for the LEDs? (I can probably work that out but I'm being lazy!)

Thanks for any help or pointers.

[Mechanised Dwarf]

Sorry I can't help but I will be watching this post - a very interesting idea. Model a micro usb sized hole with a cover so when not in use you can't even see the hole ;-)

176

[wanthony]

I imagine the two data wires will probably be useless when plugged into an AC adapter as that only supplies power. And realistically, if you plug them into a computer without doing some coding, all you'll get is a power connection from that too. So unless you're planning on incorporating a microcontroller into you're model and keeping it hooked up to your computer, all you've got is a 5V source. But don't get me wrong, it's a pretty reliable source.

 

And regards to your question about the resistors, you have to check the forward voltage and current for the LED that you're planning to use, and then use Ohm's law to figure out the resistor you'll need. For example, if you have an LED with forward voltage of 3V and current of 15 mA, you'll need a resistor that at a current of 15 mA lowers the voltage from the 5V source to 3V.

 

R = V / I = (5V-3V) / 0.015 A = 133 Ohms

 

You can round that up to the next highest resistor you can find or combine a few smaller ones, but it's always safer to have a little more resistance than necessary because most resistors will have a tolerance of ±5% anyway. So I would aim for around 140 ohms.  

 

And if you'll be using more than one LED, make sure to wire them in parallel and pair each LED with its own resistor.

 

Hope that helps!